Display screen or portion thereof with transitional graphical user interface



FIG. 1 is a front view of a first image in a sequence according to a first embodiment of our design for a display screen or portion thereof with transitional graphical user interface;

FIG. 2 is a front view of a second image in the sequence thereof;

FIG. 3 is a front view of a first image in a sequence according to a second embodiment of our design for a display screen or portion thereof with transitional graphical user interface; and,

FIG. 4 is a front view of a second image in the sequence thereof.

The appearance of the transitional image transitions between the images shown in FIG. 1-2 and between the images shown in FIG. 3-4 , respectively. The process or period in which one images transitions to another forms no part of the claimed design.

The shading in the figures is a part of the claimed design.

The outermost broken line rounded rectangle showing an electronic device illustrates environmental subject matter. The broken line showing of a display screen, and all other broken lines showing portions of the graphical user interface illustrate portions of the article. None of the aforementioned broken line subject matter forms part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 